The invention relates to the field of cooling pads for hypothermic protection of internal organs during surgery, organ transplant and the like. Methods of achieving hypothermic protection of internal organs with cooling pads are also included within the scope of the invention.
Ischemic damage to organs is a serious concern during many types of cardiovascular surgeries, organ transplants and the like. Ischemic damage is caused by the blood supply being insufficient to meet the metabolic needs of the affected organ. It is a form of local anemia. A known method of minimizing or avoiding ischemic damage is to cool the affected organ. Cooling greatly reduces the organ's rate of metabolism, and consequently, its need for oxygenated blood.
Various methods and devices have been developed to cool organs and avoid ischemic damage. A leading example is the use of cold cardioplegic solution to arrest and to cool the heart during open heart surgery to reduce its metabolic requirements. The cardioplegic solution is infused into the root of the aorta or directly into the coronary arteries. It circulates through the coronary arteries and the coronary veins, and eventually drains into the right atrium of the heart through the coronary sinus.
Another example is topical cooling of the heart. This is typically performed during open heart surgery in combination with infused cardioplegia to protect the myocardium between infusions. Topically cooling involves externally contacting at least a portion of the heart with a cold fluid or a cold surface. Topically cooling is used to augment other means of achieving hypothermia of the heart. A topical spray is described in "Topical Cardiac Cooling by Recirculation: Comparison of a Closed System Using a Cooling Pad with an Open System Using a Topical Spray," by Franklin I. Rosenfeldt and Malcolm Arnold, The Annals of Thoracic Surgery, 34(2), 138-145, 1982. A cooled saline solution is sprayed on the heart, collected, recooled and sprayed on the heart again. Another example is the use of a cooling pad through which a cooling fluid is circulated. As with the topical spray, a saline solution is cooled, brought into heat exchange relationship with the heart, recooled, and the process repeated. Such a pad is disclosed in U.S. Pat. No. 4,259,961. A similar pad for a kidney is disclosed in U.S. Pat. No. 3,738,372, and one for an entire body is disclosed in U.S. Pat. No. 3,888,259. Each of the prior art sprays and pads require an external source of cooling during use on the organ. These external heat exchangers and their connecting tubing are bulky and cumbersome in an already crowded surgical field.
Another example of topically cooling is the use of a thermal pack marketed by Minnesota Mining and Manufacturing Company, St. Paul, Minn. It contains a gel comprised of 70 weight percent water, 25 weight percent propylene glycol and 5 weight percent hydroxypropyl methylcellulose. It is not, however, recommended for such use by Minnesota Mining and Manufacturing Company.
Efforts have been made to avoid rewarming of the heart between infusions of cardioplegic solutions with passive insulation pads. Such a pad is marketed by Shiley Inc., Irvine, Calif. It is described as thin and pliable to conform to the heart and made of polyethylene foam. It is said to insulate the myocardium from the warmer descending thoracic and surrounding pericardial tissues. As a passive device, the pad must be used in combination with some form of active cooling. Typically, the pad is placed between the heart and the pericardium. The heart is then surrounded by an ice slush to provide the active cooling.